Interesting you say this as I had heard similar stories of underfunded mail crime investigations in the past. However, where I live is a very seasonal location. Population goes from 10000+ over the summer to under 1000 during the winter months.

Several years ago a couple people in the community noticed problems with their mail (mail seemingly missing, receiving wrongly addressed items, etc..). They called the postal service and an investigator was out in days. Within two weeks there were hidden cameras mounted in various locations around town pointed at mailboxes. A few more weeks and they apprehended an individual going through mailboxes based on the photos from those cameras. I don't know the final outcome, but the total turnaround from notification to arrest was less than 3 months.